Low impedance boosted high speed data cable

ABSTRACT

A high speed video cable carries signals according to the High-Definition Multimedia Interface (HDMI) or DisplayPort standards, and includes a raw cable and a boost device. The raw cable includes coaxial lines of a characteristic cable impedance lower than the impedance implied in the standards. The correct impedance is observed at the sending end by series resistors mounted in the first cable connector. The resultant loss of signal is made up with the boost device mounted in the connector at the other end of the cable.

FIELD OF THE INVENTION

The present invention relates to the construction of boosted high speed data cables, which carry high speed signal lines.

BACKGROUND OF THE INVENTION

The distribution of television signals has increasingly become based on digital methods and digitally encoded forms of video and audio signals. At the same time, higher resolution (high definition TV) has become available in the market place, commensurate with larger and higher definition displays. To meet the requirement of interconnecting such high definition displays with digital signal sources such as Digital Versatile Disc (DVD) players and receivers/decoders for digital satellite and digital cable distribution of video material, a digital interface standard has evolved, known as the High-Definition Multimedia Interface (HDMI). A detailed specification for HDMI can be obtained from the “hdmi.org” website. The HDMI specification currently available and used in this application is HDMI specification version 1.4a dated Mar. 4, 2010, which is incorporated herein by reference.

HDMI cables of various construction may be used for transmitting high speed digital signals from digital signal sources, including, but not limited to, the examples listed above, to digital displays or other equipment designed to receive signals according to the HDMI specification.

A HDMI cable carries not only four high speed differential signals which are shielded, but also a number of lower speed signals, power and ground, the whole being further shielded by an outer braid. The resulting complex cable configuration with numerous wires, some of which are individually shielded, is expensive to manufacture and terminate.

Another standard for connecting video source to a video sink, is published as the DisplayPort standard by the Video Electronics Standards Association (VESA). The latest DisplayPort specification used in this application is DisplayPort v1.2, dated Jan. 5, 2010, a copy of which may be obtained from www.vesa.org. The DisplayPort standard specifies a high speed data cable that is intended primarily to be used between a computer and its display monitor or a home-theater system. A cable meeting the DisplayPort standard is very similar to an HDMI cable, the main difference being in the respective physical connectors.

Therefore there is a need in the industry for developing an improved and easier to manufacture high speed cable, which would avoid or mitigate the shortcomings of the prior art and provides significant economies at the same time.

SUMMARY OF THE INVENTION

Therefore there is an object of the invention to provide an improved low impedance boosted high speed data cable, which would have superior properties over existing prior art cables.

According to one aspect of the invention, there is provided a digital video cable for carrying one or more high speed differential digital data signals and one or more auxiliary signals between a video source device and a video sink device according to a cable specification, the cable comprising:

-   -   a raw cable having one or more dual shielded cable elements,         each dual shielded cable element comprising a shield and two         shielded conductors for transmitting two polarities of a high         speed differential digital data signal, an impedance of at least         one dual shielded cable element being lower than a nominal         impedance of the cable specified in the cable specification;     -   a first circuit carrier connecting the video source device to         the raw cable, the first circuit carrier including two padding         resistors, each padding resistor being in series with a         respective shielded conductor of the at least one dual shielded         cable element; and     -   a second circuit carrier connecting the raw cable to the video         sink device, the second circuit carrier including a boost device         for terminating the at least one dual shielded cable element and         boosting the high speed differential digital data signal carried         by said at least one dual shielded cable element, an output of         the boost device being connected to the video sink device.

A combined resistance of the two padding resistors is substantially equal to a difference between the nominal impedance and the impedance of the at least one dual shielded cable element. Conveniently, the padding resistors are of equal resistance.

In the cable described above, said one or more dual shielded cable elements are dual coaxial elements, each comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor. Alternatively, only some of said one or more dual shielded cable elements may be dual coaxial elements, each comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor.

Alternatively, said one or more dual shielded cable elements may be Shielded Twisted Pairs (STP), each STP comprising a shield enclosing the two shielded conductors. Yet alternatively, only some of said one or more dual shielded cable elements may be Shielded Twisted Pairs (STP), each STP comprising a shield enclosing the two shielded conductors. Yet alternatively, the raw cable may comprise said one or more dual shielded cable elements only, each dual shielded element comprising a dual coaxial element, comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor, i.e. excluding any other wires between the video source device and the video sink device. Yet more alternatively, the raw cable may comprise said one or more dual shielded cable elements only, each dual shielded element comprising a Shielded Twisted Pair (STP), comprising a shield enclosing the two shielded conductors, i.e. excluding any other wires between the video source device and the video sink device.

In the embodiments of the invention, the cable specification is the High-Definition Multimedia Interface (HDMI) standard, or a DisplayPort standard.

In the embodiments of the invention, the nominal impedance of the cable is 100 ohms, and the impedance of said at least one dual shielded cable element is from about 50 ohms to about 90 ohms, comprised of characteristic impedances of the two coaxial lines. In this example, a characteristic impedance of each coaxial line may be about 35 ohms.

In another embodiment of the invention where STPs are used, the nominal impedance of the cable of 100 ohms, and characteristic impedance of a Shielded Twisted Pair is from about 50 ohms to about 90 ohms. For example, the characteristic impedance of the Shielded Twisted Pair may be about 70 ohms.

In the cable described above, a shield of one of said one or more dual shielded cable elements is adapted to carry an auxiliary signal; and the two shielded conductors of one of said one or more dual shielded cable elements are adapted to carry a high speed differential digital data signal.

The HDMI cable of the embodiments of the invention comprises: the shielded conductors of four dual shielded cable elements are extended between the video source device and the boost device; the shielded conductors of the four dual shielded cable elements are adapted to carry respective four high speed differential digital data signals, which are Transition Minimized Differential Signaling (TMDS) signals; the shielded conductors of one other dual shielded cable element, extending between the video source device and the video sink device, are adapted to carry an auxiliary signal, which is a HDMI Ethernet and Audio Return Channel (HEAC) differential signal; and the shields of the four dual shielded cable elements and said one other dual shielded cable element are adapted to carry auxiliary signals, which are Consumer Electronics Control (CEC), Serial Clock (SCL), Serial Data (SDA), Digital Data Channel (DDC)/CEC Ground, and +5V Power signals.

In the HDMI cable, the boost device may also comprises an equalizer and an amplifier for equalizing and boosting the TMDS signals respectively.

The cable of the embodiment of the invention according to the DisplayPort specification has been designed as follows: the shielded conductors of four dual shielded cable elements are extended between the video source device and the boost device; the shielded conductors of the four dual shielded cable elements are adapted to carry respective four high speed differential digital data signals, which are Main Line lanes; the shielded conductors of one other dual shielded cable element, extending between the video source device and the video sink device, are adapted to carry an auxiliary signal, which is an Auxiliary Channel (AUX CH) differential signal; and the shields of the four dual shielded cable elements and said one other dual shielded cable element are adapted to carry auxiliary signals, which are CONFIG1, CONFIG2, Ground, Hot Plug Detect (HPD), and DisplayPort power (DP_PWR) signals.

The Display Port cable of the embodiments of the present invention, the boost device may also comprise an equalizer and an amplifier for equalizing and boosting the Main Line lanes respectively.

According to yet another aspect of the invention, there is provided a method for transmitting a high speed differential digital data signal from a video source device to a video sink device over a digital video cable designed to meet a cable specification, the method comprising:

-   -   coupling, through two respective padding resistors, two         polarities of the high speed differential digital data signal to         an input of a raw cable, which has an impedance lower than a         nominal impedance of the cable specified in the cable         specification;     -   coupling a differential output signal from an output of the raw         cable to a boost device whose input matches the impedance of the         raw cable;     -   boosting the differential output signal to generate a boosted         differential signal; and     -   coupling the boosted differential signal to the video sink         device.

The method further includes transmitting an auxiliary signal from the video source device to the video sink device over a shield of the raw cable. In the method described above, the transmitting comprises transmitting over a coaxial cable having a pair of coaxial lines whose shields are joined; including transmitting the auxiliary signal over the joined shields.

Alternatively, the transmitting may comprise transmitting over a Shielded Twisted Pair (STP) comprising a shield enclosing two shielded conductors, including transmitting the auxiliary signal over the shield of the STP, and transmitting the high speed differential digital data signal over the two shielded conductors.

Thus, an improved low impedance boosted high speed data cable a method of transmitting digital signals over the cable have been provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1A shows a simplified boosted cable 10 to illustrate the principle of transmitting a single-ended signal and a differential signal over a shielded cable comprising a dual shielded cable element 12, which is a Shielded Twisted Pair (STP), and a boost circuit 20;

FIG. 1B shows a dual coaxial element 12B that may be used instead of the dual shielded cable element 12 of FIG. 1A;

FIG. 2 shows a configuration 100 of a generic Boosted Digital Video Cable 102.j which may be of any one “j” of a number of types according to embodiments of the invention, interconnecting a Video Source Device (Tx) 104 and a Video Sink Device (Rx) 106;

FIG. 3 shows a Basic Coax HDMI Cable 102.1 based on coax technology according to a first embodiment of the invention;

FIG. 4 shows a Basic STP HDMI Cable 102.2 based on Shielded Twisted Pair (STP) technology according to a second embodiment of the invention;

FIG. 5 shows a HEAC-Capable Coax HDMI Cable 102.3 based on coax technology according to a third embodiment of the invention;

FIG. 6 shows a HEAC-Capable STP HDMI Cable 102.4 based on Shielded Twisted Pair (STP) technology according to a fourth embodiment of the invention;

FIG. 7 shows a Coax DisplayPort Cable 102.5 based on coax technology according to a fifth embodiment of the invention;

FIG. 8 shows a STP DisplayPort Cable 102.6 based on Shielded Twisted Pair (STP) technology according to a sixth embodiment of the invention;

FIG. 9 shows a three coax line cross sections, to illustrate a comparison between exemplary design choices, including a standard coax 902; a reduced-outer-diameter coax 904; and an increased-core-diameter coax 906; and

FIG. 10 shows a Low-Impedance (Low Z0) Coax HDMI Cable 102.10 which is identical to the Basic Coax HDMI Cable 102.1 of FIG. 3 except for a Low-Impedance Input Paddle Board 114.10 which replaces the first Input Paddle Board 114.1.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

Embodiments of the present invention describe a boosted high speed cable comprising shielded high speed signal lines and carrying other signals of lower speed as well as power and ground, in which the shields of the shielded high speed signal lines are used in carrying the lower speed signals and power and ground.

The inherent characteristics and manufacturing imperfections of high-speed differential signaling cables such as may be used to carry HDMI signals have an adverse effect on the high-speed signals carried by the cable. To mitigate these effects, various boosted high speed data cables have been proposed by the industry. For example, in the previously filed US application of the same assignee, Ser. No. 11/826,713 filed on Jul. 18, 2007, a boost device is embedded in the cable, the contents of the patent application being incorporated herein by reference.

The inventors have discovered that the boost device may not only be used to equalize and boost the signal, as described in the U.S. application Ser. No. 11/826,713 cited above, but may also be used to advantage in other ways, specifically to allow the individual shields of the differential high speed signals to be used for carrying other signals.

In a cable of the prior art, the shields are all tied to ground in an effort to reduce electro-magnetic interference (EMI). In a cable according to any of the embodiments of the invention, EMI shielding is still provided, but instead of tying the shields of the high-speed HDMI signals to ground, the lower speed signals as well as power and ground, are sent over the shields.

FIG. 1A shows a simplified boosted cable 10 to illustrate the principle of transmitting a single-ended signal and a differential signal over a shielded cable. The simplified boosted cable 10 comprises a dual shielded cable element 12 which is a Shielded Twisted Pair (STP) including a single shield 14 enclosing first and second signal wires (two shielded conductors) 16 and 18 respectively, and a boost circuit 20 having inputs i+ and i− and outputs o+ and o−. The inputs i+ and i− of the boost circuit 20 are a differential input pair and the outputs o+ and o− of the boost circuit 20 are a differential output pair.

The simplified boosted cable 10 receives a single-ended signal “A” and a differential signal “D” comprising polarities D+i and D−i at the input of the simplified boosted cable 10, and is designed to deliver these signals substantially undistorted at its output. The boost circuit 20 includes an equalizer circuit (EQ) and a differential amplifier (Amp) for equalizing and boosting the differential signal “D”.

The signal wires 16 and 18 carry the differential signal “D”, comprising polarities D+i and D−i respectively from the input of the simplified boosted cable 10 through the dual shielded cable element 12 to the inputs i+ and i− of the boost circuit 20. The outputs o+ and o− of the boost circuit 20 deliver a processed differential signal comprising polarities D+o and D−o to the output of the simplified boosted cable 10, which represent the differential signal “D”.

The single shield 14 carries a single-ended signal “A” directly from the input of the simplified boosted cable 10 to its output.

The processing functions of the boost circuit 20 include: receiving the differential input signal; removing any common mode component of the differential input signal; equalizing the signal to compensate for signal impairments introduced by the dual shielded cable element 12; and outputting a boosted version of the equalized differential signal “D”.

To summarize, the differential signal is a high-speed data signal “D”, which may benefit from equalization and boosting while the single-ended signal “A” may be a ground signal, a power supply signal, or any low speed signal which does not require equalization or boosting.

Along the length of the STP raw cable 12, a small fraction of the single-ended signal “A” is unavoidably coupled as undesirable noise through distributed capacitances 22 and 24 into the signal wires 16 and 18 respectively, thus affecting the differential signal “D”. Given that, by the construction of the dual shielded cable element 12, the capacitances 22 and 24 are essentially equal, the polarities D+i and D−i respectively are equally affected, and the coupled noise manifests itself as common mode noise.

At the receiving end of the dual shielded cable element 12, the boost circuit 20 receiving the differential signal “D”, provides sufficient common-mode rejection such that the common mode noise is not converted into a differential signal. The ouputs o+ and o− of the boost circuit 20, that produces a boosted signal, is then a clean differential signal which is delivered at the output of the simplified boosted cable 10.

Alternatively, as shown in FIG. 1B, a dual coaxial element 12B may be used instead of the dual shielded cable element 12. The dual coaxial element 12B is comprised of two coaxial lines 26 and 28 forming a coax pair 30 whose outer conductors (shields) are joined together, the joined shields providing the connection for the single-ended signal “A”. The coaxial line 26 carries the polarity D+i of the differential signal “D” on its inner conductor 32, while the coaxial line 28 carries the polarity D−i of the differential signal “D” on its inner conductor 34. Coupling between the single-ended signal “A” and the inner conductors 32 and 34 which are also referred to as shielded conductors, through distributed capacitances 36 and 38 respectively is analogous to the case of the dual shielded cable element 12, resulting in common mode noise only which is rejected by the boost circuit 20.

In the following figures, various boosted HDMI cable configurations are shown which are embodiments of the invention that are based on the cable elements described in FIGS. 1A and 1B.

FIG. 2 shows a configuration 100 of a generic Boosted Digital Video Cable 102.j which may be of any of a number of types to be described below, connecting a Video Source Device (Tx) 104 to a Video Sink Device (Rx) 106. The Boosted Digital Video Cable 102.j comprises a Raw Cable 108.j, and Input and Output Connectors 110 and 112 respectively.

The Input Connector 110 connects the Raw Cable 108.j to the Video Source Device (Tx) 104, and comprises an Input Paddle Board 114.j for providing connectivity between signals from the Video Source Device (Tx) 104 and facilities (wires, shields) of the Raw Cable 108.j.

The Raw Cable 108.j includes dual shielded cable elements and optionally a single coaxial line, for carrying the video signals which are high speed differential data signals as well as auxiliary signals as defined by cable specifications. Alternatively, the raw cable may include dual shielded cable elements only, i.e. excluding any other wires between the video source device and the video sink device.

Various embodiments of the Raw Cable 108.j are described below, covering HDMI and DisplayPort specifications and using either coaxial or shielded twisted pair (STP) technology.

The Output Connector 112 connects the Raw Cable 108 to the Video Sink Device (Rx) 106, and comprises an Output Paddle Board 116.j including a Cable Boost Device 118, for providing connectivity between the facilities (wires, shields) of the Raw Cable 108.j and the Video Sink Device (Rx) 106. The Cable Boost Device 118 is connected between some of the wires of the cable and the input of the Video Sink Device (Rx) 106. The Cable Boost Device 118 includes a number of Boost Circuits 20, one Boost Circuit 20 for terminating the dual shielded cable elements of the Raw Cable 108 which carry the high speed differential digital data signals that arrive from the Video Source Device (Tx) 104 over the Raw Cable 108.

The Input Paddle Board 114.j and the Output Paddle Board 116.j constitute first and second circuit carriers which are conveniently constructed as small printed circuit boards (PCB) and may be configured to provide the mechanical support for connector contacts according to the cable specification, for example according to the HDMI or DisplayPort standards.

FIG. 3 shows a Basic Coax HDMI Cable 102.1 based on coax technology, including a circuit carrier in the form of a first Input Paddle Board 114.1, a first Raw Cable 108.1, and a first Output Paddle Board 116.1 according to an embodiment of the invention. The first Raw Cable 108.1 includes a total of nine individual coaxial lines arranged as four dual shielded cable elements, that is coax pairs 202, 204, 206 and 208, and a single coaxial line 210. Each coax pair 202 to 208 comprises two coaxial lines with inner signal wires labeled as “a” and “b”, and two shields which are joined together such that the joined shields form a single conductive path. Thus, each of the coax pairs 202 to 208 provides three electrical connections, i.e. one differential connection (wires “a” and “b”) and one single-ended connection (the joined shields), as described earlier (see FIG. 1B). The single coaxial line 210 provides only two conductive paths, the inner signal wire “a” and the shield.

The Cable Boost Device 118 is comprised within the first Output Paddle Board 116.1, and has high speed differential signal inputs D2 (polarities D2+, D2−), D1 (D1+, D1−), D0 (D0+, D0−), and D3 (D3+, D3−) and corresponding boosted outputs C2 (polarities C2+, C2−), C1 (C1+, C1−), C0 (C0+, C0−), and C3 (C3+, C3−). In addition, the Cable Boost Device 118 has ground and power inputs (GND, +5V), and a programming input (Pgm). The programming input is used to program parameters of the Cable Boost Device 118 in manufacturing. In normal operation this input is not active, and is effectively grounded (connected to GND) through a low resistance within the Cable Boost Device 118.

HDMI signals may be classified as either high speed differential data signals or auxiliary signals. The high speed differential data signals include Transition Minimized Differential Signaling (TMDS) Data 0, TMDS Data 1, TMDS Data 2, and TMDS Clock. The auxiliary signals are the following single ended signals: Consumer Electronics Control (CEC), Serial Clock (SCL), Serial Data (SDA), Utility, and Hot Plug Detect (HPD). A +5V Power and a Digital Data Channel (DDC)/CEC Ground connection is also provided through the cable. The +5V Power and the DDC/CEC Ground connections are included in the auxiliary signals for simplicity here.

The signals from the Video Source Device (Tx) 104 are connected to terminals in an Input Connection Field 212 of the Basic Coax HDMI Cable 102.1, and recovered at the opposite end of the cable with terminals of an Output Connection Field 214 for transmission to the Video Sink Device (Rx) 106. Standard HDMI signal names and corresponding terminal labels of the Input and Output Connection Fields 212 and 214 are listed in Table 1, which shows the preferred connection arrangement, or signal allocation scheme, for the Basic Coax HDMI Cable 102.1.

Referring to FIG. 3 and Table 1, each of the four HDMI high speed differential data signals, TMDS Data 0, TMDS Data 1, TMDS Data 2, and TMDS Clock, are routed through the Basic Coax HDMI Cable 102.1 as described in the following:

The TMDS Data 2 differential signal, comprising TMDS Data2+ and TMDS Data2− is:

-   -   connected from the Video Source Device (Tx) 104 to txD2+ and         txD2− terminals in the Input Connection Field 212;     -   routed in the first Input Paddle Board 114.1 to the input of the         raw cable, namely the inner signal wires “a” and “b” of the coax         pair 202;     -   routed through the inner signal wires “a” and “b” of the coax         pair 202 of the first Raw Cable 108.1;     -   coupled from the end of the first Raw Cable 108.1 to D2+ and D2−         inputs of the Cable Boost Device 118 in the first Output Paddle         Board 116.1; and     -   coupled from the C2+ and C2− outputs of the Cable Boost Device         118 to rxD2+ and rxD2− terminals in the Output Connection Field         214.

The other three HDMI high speed differential data signals (TMDS Data 0, TMDS Data 1, and TMDS Clock) are similarly connected, see Table 1.

The shields of the HDMI high speed data signals (TMDS Data0 Shield, TMDS Data1 Shield, TMDS Data2 Shield, and TMDS Clock Shield), as well as the DDC/CEC Ground signal from the Video Source Device (Tx) 104 are connected to terminals txD0 s, txD1 s, txD2 s, txCKs, and txGnd of the Input Connection Field 212, and tied to an input common ground node 216 in the first Input Paddle Board 114.1 whence the input common ground node 216 is connected to the shield of the single coaxial line 210.

In the first Output Paddle Board 116.1, the shield of the single coaxial line 210 is connected to an output common ground node 218 which is further connected to the ground (GND) input of the Cable Boost Device 118, and to shield and ground connections of the Video Sink Device (Rx) 106, namely terminals rxD0 s, rxD1 s, rxD2 s, and rxGnd. The TMDS Clock Shield of the Video Sink Device (Rx) 106 is connected through a terminal rxCKs to the programming (Pgm) input of the Cable Boost Device 118, and so is indirectly grounded through the small resistance within the Cable Boost Device 118. This allows the Cable Boost Device 118 to be programmed from the HDMI connector after the boosted cable is assembled without requiring any additional wire to access it. Alternatively, the rxCKs terminal may be grounded directly at the output common ground node 218 along with the other shield connections.

The remaining auxiliary signals (CEC, SCL, SDA, Utility, +5V Power, and HPD), are connected in the first Input Paddle Board 114.1 to terminals txCEC, txSCL, txSDA, txUt, txPWR, and txHPD respectively. In the first Output Paddle Board 116.1, they are connected to terminals rxCEC, rxSCL, rxSDA, rxUt, rxPWR, and rxHPD respectively. Compared to the HDMI high speed data signals which are boosted by the Boost Device 118, these auxiliary HDMI signals are at a lower speed, bypass the Cable Boost Device 118, and may be carried on the inner wires or over the shields of the coaxial lines as may be convenient. The “Utility” signal in this case is unused. However if it is necessary to include it, it may be carried on an additional inner wire or over the shield of a coaxial wire as way be convenient.

While four of the auxiliary signals CEC, SCL, +5V Power and HPD are carried over the shields of the coax pairs 202 to 208, another auxiliary signal (DDC/CEC Ground), to which also the shields of the TMDS signals are tied) is carried over the shield of single coaxial line 210, and yet another auxiliary signal (SDA), is carried over the inner signal wire “a” of the single coaxial line 210.

In the Basic Coax HDMI Cable 102.1, these remaining HDMI signals (except the Utility signal) are carried over the cable as follows:

-   -   CEC from the terminal txCEC, over the combined shields of the         coax pair 202, to the terminal rxCEC;     -   SCL from the terminal txSCL, over the combined shields of the         coax pair 204, to the terminal rxSCL;     -   SDA from the terminal txSDA, over the inner wire “a” of the coax         210, to the terminal rxSDA;     -   +5V Power from the terminal txPWR, over the combined shields of         the coax pair 206, to the terminal rxPWR; and     -   Hot Plug Detect from the terminal txHPD, over the combined         shields of the coax pair 208, to the terminal rxHPD.

In the first Output Paddle Board 116.1 the +5V Power is also connected to the power input (+5V) of the Boost Device 218.

TABLE 1 Preferred Signal Routing in Basic Coax HDMI Cable 102.1 Input Boost Boost Output HDMI Connec- Raw Cable Device Device Connec- Signal Name tion 212 108.1 Input Output tion 214 TMDS Data2 txD2s 210.shield --> --> rxD2s Shield TMDS Data2+ txD2+ 202.a D2+ C2+ rxD2+ TMDS Data2− txD2− 202.b D2− C2− rxD2− TMDS Data1 txD1s 210.shield --> --> rxD1s Shield TMDS Data1+ txD1+ 204.a D1+ C1+ rxD1+ TMDS Data1− txD1− 204.b D1− C1− rxD1− TMDS Data0 txD0s 210.shield --> --> rxD0s Shield TMDS Data0+ txD0+ 206.a D0+ C0+ rxD0+ TMDS Data0− txD0− 206.b D0− C0− rxD0− TMDS Clock txCKs 210.shield — — — Shield Pgm --> rxCKs TMDS Clock+ txCK+ 208.a D3+ C3+ rxCK+ TMDS Clock− txCK− 208.b D3− C3− rxCK− DDC/CEC txGnd 210.shield GND --> rxGnd Ground CEC txCEC 202.shield --> --> rxCEC SCL txSCL 204.shield --> --> rxSCL SDA txSDA 210 --> --> rxSDA Utility txUt n/c — — rxUt +5 V Power txPWR 206.shield +5 V --> rxPWR Hot Plug Detect txHPD 208.shield --> --> rxHPD

FIG. 4 shows a Basic STP HDMI Cable 102.2 based on Shielded Twisted Pair (STP) technology, including a second Input Paddle Board 114.2, a second Raw Cable 108.2, and a second Output Paddle Board 116.2 according to another embodiment of the invention.

The Input and Output Connection Fields 212 and 214, including the respective terminals remain unchanged from the Basic Coax HDMI Cable 102.2. The second Raw Cable 108.2 comprises five Shielded Twisted Pairs (STPs) 302, 304, 306, 308, and 310, each comprising a shield and two signal wires “a” and “b” as described in FIG. 1A. The allocation of the standard HDMI signals to connections through the second Raw Cable 108.2 is provided by configurations of the second Input and Output Paddle Boards 114.2 and 116.2 respectively.

The STPs 302, 304, 306, 308, and 310 of the second Raw Cable 108.2 provide 15 (3×5) distinct conductive paths, compared to the 14 paths (3×4+1) of the first Raw Cable 108.1. Hence an additional path is available which is advantageously used in a modification of the signal assignments. This is illustrated in FIG. 4 as well as in Table 2 which lists the preferred arrangement for the Basic STP HDMI Cable 102.2.

Because of the additional line available in the second Raw Cable 108.2, compared to the first Raw Cable 108.1, it is possible to use a shield connection (a common node 312 connected to the shield of the STP 308) to connect the shields of all high speed signals (D0, D1, D2, and CK), and use a separate shield connection (the shield of the STP 310) for the ground connection.

The preferred assignments shown in Tables 1 and 2 are to some extent arbitrary, and may be adapted to best utilize the space on the paddle boards and the configurations of the respective connectors.

TABLE 2 Preferred Signal Routing in Basic STP HDMI Cable 102.2 Input Boost Boost Output HDMI Connec- Raw Cable Device Device Connec- Signal Name tion 212 108.2 Input Output tion 214 TMDS Data2 txD2s 308.shield --> --> rxD2s Shield TMDS Data2+ txD2+ 302.a D2+ C2+ rxD2+ TMDS Data2− txD2− 302.b D2− C2− rxD2− TMDS Data1 txD1s 308.shield --> --> rxD1s Shield TMDS Data1+ txD1+ 304.a D1+ C1+ rxD1+ TMDS Data1− txD1− 304.b D1− C1− rxD1− TMDS Data0 txD0s 308.shield --> --> rxD0s Shield TMDS Data0+ txD0+ 306.a D0+ C0+ rxD0+ TMDS Data0− txD0− 306.b D0− C0− rxD0− TMDS Clock txCKs 308.shield — — — Shield Pgm --> rxCKs TMDS Clock+ txCK+ 308.a D3+ C3+ rxCK+ TMDS Clock− txCK− 308.b D3− C3− rxCK− DDC/CEC txGnd 310.shield GND --> rxGnd Ground CEC txCEC 306.shield --> --> rxCEC SCL txSCL 310 --> --> rxSCL SDA txSDA 310.b --> --> rxSDA Utility txUt n/c — — rxUt +5 V Power txPWR 302.shield +5 V --> rxPWR Hot Plug Detect txHPD 304.shield --> --> rxHPD

In this embodiment of the invention, the raw cable includes STPs only, i.e. excluding any other wires between the video source device and the video sink device.

HEAC Capability

In a Supplement 2 to the HDMI specification version 1.4. dated Jun. 5, 2009 cited above, a “HDMI Ethernet and Audio Return Channel” (HEAC) is specified. The HEAC channel is carried in a HEAC-capable HDMI cable as a differential data signal, i.e. negative and positive polarity signals HEAC− and a HEAC+ respectively, which replace the Hot Plug Detect (HPD) signal and the previously unused “Utility” signal respectively of the standard HDMI signal set. The HEAC channel is a passive channel which does not require boosting by the Cable Boost Device 118. However, it does require careful control of its impedance and should therefore be enclosed in a shield, either by running each polarity in a coaxial line, or both polarities over a shielded twisted pair (STP). Accordingly, only modified connectivity (adding the HEAC channel, with controlled impedance lines, replacing HPD and “Utility” signals) in the paddle boards and in the raw cable are required to convert the basic HDMI Cables (102.1 and 102.2) to accommodate the HEAC channel.

FIG. 5 shows a HEAC-Capable Coax HDMI Cable 102.3 based on coax technology, and capable of carrying an HEAC channel: including a third Input Paddle Board 114.3, a third Raw Cable 108.3, and a third Output Paddle Board 116.3 according to yet another embodiment of the invention.

The signals of the HEAC-capable HDMI signal set from the Video Source Device (Tx) 104, are connected to a HEAC-capable Input Connection Field 412 of the HEAC-Capable Coax HDMI Cable 102.3, and recovered at the opposite end of the cable with a HEAC-capable Output Connection Field 414 for transmission to the Video Sink Device (Rx) 106. The modifications of the HEAC-capable Input and Output Fields 412 and 414 relate to name changes compared to the Input and Output Fields 212 and 214, and reflect name changes of the terminals concerned: txUt, rxUt, txHPD, and rxHPD of the Input and Output Fields 212 and 214, become txHEAC−, rxHEAC−, txHEAC+, and rxHEAC+ of the HEAC-capable Input and Output Fields 412 and 414.

The third Raw Cable 108.3 comprises a total of ten individual coaxial lines arranged in four dual shielded cable elements, that is coax pairs 402, 404, 406, and 408, for carrying high speed digital data signals, and another dual shielded cable element, that is a coax pair 410, for carrying a differential auxiliary signal. Each coax pair 402 to 410 includes two coaxial lines with inner signal wires labeled as “a” and “b”, and two shields which are joined together such that the joined shields of each coax pair form a single conductive path. Thus, each of the coax pairs 402 to 410 provides three electrical connections, i.e. one differential connection (wires “a” and “b”) and one single-ended connection (the joined shields), as described earlier (see FIG. 1B).

The assignments of the HDMI signals to the available cable connections in the third Input Paddle Board 114.3 and the third Output Paddle Board 116.3 are similar compared to the assignments used in the first Input and Output Paddle Boards 114.1 and 116.1 respectively. Unchanged connections are those for the differential HDMI high-speed data channels TMDS D2, D1, D0, and Clock, incoming from the Video Source Device 104, which are connected through the coax pairs 402, 404, 406, and 408 respectively to corresponding inputs of the Cable Boost Device 118.

The differential HEAC channel is connected through the coax pair 410, and bypasses the Cable Boost Device 118. The shields of the coax pairs 402, 404, 406, 408, and 410 serve as conductors for the HDMI signals CEC, SCL, +5V Power, SDA, and DDC/CEC Ground respectively.

TABLE 3 Preferred Signal Routing in HEAC-capable Coax HDMI Cable 102.3 Input Boost Boost Output HDMI Connec- Raw Cable Device Device Connec- Signal Name tion 212 108.2 Input Output tion 214 TMDS Data2 txD2s 410.shield --> --> rxD2s Shield TMDS Data2+ txD2+ 402.a D2+ C2+ rxD2+ TMDS Data2− txD2− 402.b D2− C2− rxD2− TMDS Data1 txD1s 410.shield --> --> rxD1s Shield TMDS Data1+ txD1+ 404.a D1+ C1+ rxD1+ TMDS Data1− txD1− 404.b D1− C1− rxD1− TMDS Data0 txD0s 410.shield --> --> rxD0s Shield TMDS Data0+ txD0+ 406.a D0+ C0+ rxD0+ TMDS Data0− txD0− 406.b D0− C0− rxD0− TMDS Clock txCKs 410.shield — — — Shield Pgm --> rxCKs TMDS Clock+ txCK+ 408.a D3+ C3+ rxCK+ TMDS Clock− txCK− 408.b D3− C3− rxCK− DDC/CEC txGnd 410.shield GND --> rxGnd Ground CEC txCEC 402.shield --> --> rxCEC SCL txSCL 404.shield --> --> rxSCL SDA txSDA 408.shield --> --> rxSDA HEAC− txHEAC+ 410 --> --> rxHEAC− +5 V Power txPWR 406.shield +5 V --> rxPWR HEAC+ txHEAC+ 410.b --> --> rxHEAC+

The incoming shields of the HDMI high-speed data channels TMDS D2, D1, D0, and the TMDS Clock, are tied to the DDC/CEC Ground connection through the shield of the coax pair 410 of the cable, thus providing a connection to the outgoing shields of the HDMI high-speed data channels TMDS D2, D1, and D0. The outgoing shield of the TMDS Clock (rxCKs) is connected to the programming pin (Pgm) of the Cable Boost Device 118 as described above with reference to the Basic Coax HDMI Cable 102.1.

The preferred HDMI signal routing of the HEAC-Capable Coax HDMI Cable 102.3 is listed in Table 3.

FIG. 6 shows a HEAC-Capable STP HDMI Cable 102.4, based on Shielded Twisted Pair (STP) technology and capable of carrying an HEAC channel, including a fourth Input Paddle Board 114.4, a fourth Raw Cable 108.4, and a fourth Output Paddle Board 116.4 according to a fourth embodiment of the invention.

The HEAC-capable Input and Output Connection Fields 412 and 414 of the HEAC-Capable STP HDMI Cable 102.4, including the respective terminals remain unchanged from the HEAC-Capable Coax HDMI Cable 102.3. The fourth Raw Cable 108.4 comprises five Shielded Twisted Pairs (STPs) 502, 504, 506, 508, and 510, each comprising a shield and two signal wires “a” and “b” as described in FIG. 1A. The allocation of the HDMI signals to connections through the fourth Raw Cable 108.4 is provided by configurations of the fourth Input and Output Paddle Boards 114.4 and 116.4 respectively.

The STPs 502, 504, 506, 508, and 510 of the fourth Raw Cable 108.4 provide 15 (3×5) distinct conductive paths, the same number as provided in the third Raw Cable 108.3. Accordingly, an analogous allocation of the individual signals to the Shielded Twisted Pairs including their shields, could be made. Similarly, part of the allocation scheme could also be “borrowed” from the other STP based embodiment (the Basic STP HDMI Cable 102.2) and suitably modified to accommodate the HEAC signal.

A different connection allocation scheme is proposed here to illustrate the considerable latitude available in choosing configurations. The preferred assignments for the HEAC-Capable STP HDMI Cable 102.4 are illustrated in FIG. 6 as well as in Table 4.

As indicated earlier, the preferred assignments of signal leads in the cables are shown in the Tables 1, 2, 3, and 4. These are to some extent arbitrary. The “+5V Power” and the “DDC/CEC Ground” connections are preferably carried on a shield; the HDMI high speed data signals (TMDS D0, D1, D2, and Clock) should always be carried on shielded conductors, i.e. the inner conductors of coax lines or the twisted signal wires of STPs, depending on wire type; and the lower speed connections (CEC, SCL, SDA, Utility, and HPD) may be carried on inner/signal wires or shields in an arrangement that may be adapted to best utilize the space on the paddle boards and the configuration of the respective connectors.

The use of the TMDS Clock Shield connection on the receive side (rxCKs) to access the programming pin (Pgm) of the Cable Boost Device 118 is a convenience for programming the device in the fully assembled boosted HDMI cable. If this feature is not required, the TMDS Clock Shield should be grounded along with the other TDMS signal shields at both ends of the cable.

TABLE 4 Preferred Signal Routing in HEAC-capable STP HDMI Cable 102.4 Input Boost Boost Output HDMI Connection Raw Cable Device Device Connec- Signal Name 212 108.2 Input Output tion 214 TMDS Data2 txD2s 510.shield --> --> rxD2s Shield TMDS Data2+ txD2+ 502.a D2+ C2+ rxD2+ TMDS Data2− txD2− 502.b D2− C2− rxD2− TMDS Data1 txD1s 510.shield --> --> rxD1s Shield TMDS Data1+ txD1+ 504.a D1+ C1+ rxD1+ TMDS Data1− txD1− 504.b D1− C1− rxD1− TMDS Data0 txD0s 510.shield --> --> rxD0s Shield TMDS Data0+ txD0+ 506.a D0+ C0+ rxD0+ TMDS Data0− txD0− 506.b D0− C0− rxD0− TMDS Clock txCKs 510.shield — — — Shield Pgm --> rxCKs TMDS Clock+ txCK+ 508.a D3+ C3+ rxCK+ TMDS Clock− txCK− 508.b D3− C3− rxCK− DDC/CEC txGnd 510.shield GND --> rxGnd Ground CEC txCEC 506.shield --> --> rxCEC SCL txSCL 508.shield --> --> rxSCL SDA txSDA 504.shield --> --> rxSDA HEAC− txHEAC--> 510 --> --> rxHEAC− +5 V Power txPWR 502.shield +5 V --> rxPWR HEAC+ txHEAC+ 510.b --> --> rxHEAC+ DisplayPort Cables

FIG. 7 shows a Coax DisplayPort Cable 102.5 based on coax technology, including a fifth Input Paddle Board 114.5, a fifth Raw Cable 108.5, and a fifth Output Paddle Board 116.5 according to an embodiment of the invention. The fifth Raw Cable 108.5 includes a total of ten individual coaxial lines arranged in five coax pairs 602, 604, 606, 608, and 610. Each coax pair 602 to 610 comprises two coaxial lines with inner signal wires labeled as “a” and “b”, and two shields which are joined together such that the joined shields form a single conductive path. Thus, each of the coax pairs 602 to 608 provides three electrical connections, i.e. one differential connection (wires “a” and “b”) and one single-ended connection (the joined shields), as described earlier (see FIG. 1B).

The same Cable Boost Device 118 as in the boosted HDMI cables described above, is comprised within the fifth Output Paddle Board 116.5.

Standard DisplayPort signals from the Video Source Device (Tx) 104, are connected to terminals in a DisplayPort Input Connection Field 612 of the Coax DisplayPort Cable 102.5, and recovered at the opposite end of the cable at terminals of a DisplayPort Output Connection Field 614 for transmission to the Video Sink Device (Rx) 106. The DisplayPort signal names and corresponding terminal labels of the DisplayPort Input and Output Connection Fields 612 and 614 are listed in Table 5, which shows the preferred connection arrangement, or signal allocation scheme, for the Coax DisplayPort Cable 102.5.

Referring to FIG. 7 and Table 5, each of the four DisplayPort high speed differential data lanes ML-L0, ML-L1, ML-L2, and ML-L3, is routed through the Coax DisplayPort Cable 102.5 as described in the following:

The Main Line Lane0 differential signal, comprising positive (p) and negative (n) polarities is:

-   -   connected from the Video Source Device (Tx) 104 to txML_L0+ and         txML_L0− terminals in the DisplayPort Input Connection Field         612;     -   routed in the fifth Input Paddle Board 114.5 to the inner signal         wires “a” and “b” of the coax pair 602;     -   routed through the fifth Raw Cable 108.5 on the inner signal         wires “a” and “b” of the coax pair 602 of the fifth Raw Cable         108.5;     -   coupled from the end of the fifth Raw Cable 108.5 to D0+ and D0−         inputs of the Cable Boost Device 118 in the fifth Output Paddle         Board 116.5; and     -   coupled from the C0+ and C0− outputs of the Cable Boost Device         118 to rxML_L0+ and rxML_L0− terminals in the DisplayPort Output         Connection Field 614.

The other three main-line differential data signals (Main Line Lane1, Lane2, and Lane 3) are similarly connected, see Table 5.

All ground connections of the incoming DisplayPort connector which are labeled txGND0, txGND1, txGND2, txGND3, txGNDaux as well as the “Return” (txGNDpwr), i.e. the power return terminal, are tied together to an input common ground node 616 in the fifth Input Paddle Board 114.5, and connected to the shield of the coax pair 604.

In the fifth Output Paddle Board 116.5, the shield of the coax pair 604 is connected to an output common ground node 618 which is also connected to the ground (GND) input of the Cable Boost Device 118, and to shield and ground connections of the Video Sink Device (Rx) 106, namely terminals rxGND0, rxGND1, rxGND2, rxGNDaux, and txGNDpwr. An exception is the fourth ground pin of the receive side which is connected through a terminal rxGND3 to the programming (Pgm) input of the Cable Boost Device 118, and so is only indirectly grounded. This allows the Cable Boost Device 118 to be programmed from the connector after the boosted cable is assembled without requiring any additional wire to access it. Alternatively, the rxGND3 terminal may also be grounded at the output common ground node 618 along with the other ground connections.

Other DisplayPort signals CONFIG1, CONFIG2, AUX Channel (p) and (n), Hot Plug, and DP_PWR, are respectively connected in the fifth Input Paddle Board 114.5 to terminals txCONFIG1, txCONFIG2, txAuxCh+ and txAuxCh−, txHPD, and txDP_PWR. In the fifth Output Paddle Board 116.5. they are respectively connected to terminals rxCONFIG1, rxCONFIG2, rxAuxCh+ and rxAuxCh−, rxHPD, and rxDP_PWR. Compared to the main line high speed signals which are boosted by the Boost Device 118, these other DisplayPort signals are at a lower speed, bypass the Cable Boost Device 118, and may be carried on the inner wires or over the shields of the coaxial lines as may be convenient. The AUX Channel signal however is of moderately high speed and is required to be carried in a controlled impedance wire, for which the coax pair 610 is chosen in this embodiment of the invention.

In the Coax DisplayPort Cable 102.5, the remaining signals are carried over the cable as follows:

-   -   CONFIG1 from the terminal txCONFIG1, over the combined shields         of the coax pair 606, to the terminal rxCONFIG1;     -   CONFIG2 from the terminal txCONFIG2, over the combined shields         of the coax pair 608, to the terminal rxCONFIG2;     -   Hot Plug from the terminal txHPD, over the combined shields of         the coax pair 610, to the terminal rxHPD; and     -   DP_PWR from the terminal txDP_PWR, over the combined shields of         the coax pair 602, to the terminal rxDP_PWR.

In the fifth Output Paddle Board 116.5 the DP_PWR is also connected to the power input (+5V) of the Cable Boost Device 218. Even though the voltage of DP_PWR will be lower than the HDMI +5V Power, the same Cable Boost Device 218 may be designed or programmed to run at both the HDMI and the DisplayPort voltages. Alternatively, a DisplayPort specific version of the Cable Boost Device 218 may be developed.

TABLE 5 Preferred Signal Routing in Coax DisplayPort Cable 102.5 Input Boost Boost Output DisplayPort Connec- Raw Cable Device Device Connec- Signal Name tion 212 108.1 Input Output tion 214 Main Line txML_L0+ 602 D0+ C0+ rxML_L0+ Lane0 (p) Ground txGND0 604.shield --> --> rxGND0 (pin 2) Main Line txML_L0− 602.b D0− C0− rxML_L0− Lane0 (n) Main Line txML_L1+ 604 D1+ C1+ rxML_L1+ Lane1 (p) Ground txGND1 604.shield --> --> rxGND1 (pin 5) Main Line txML_L1− 604.b D1− C1− rxML_L1− Lane1 (n) Main Line txML_L2+ 606 D2+ C2+ rxML_L2+ Lane2 (p) Ground txGND2 604.shield --> --> rxGND2 (pin 8) Main Line txML_L2− 606.b D2− C2− rxML_L2− Lane2 (n) Main Line txML_L3+ 608 D3+ C3+ rxML_L3+ Lane3 (p) Ground txGND3 604.shield Pgm --> rxGND3 (pin 11) Main Line txML_L3− 608.b D3− C3− rxML_L3− Lane0 (n) CONFIG1 txCONFIG1 606.shield --> --> rxCONFIG1 CONFIG2 txCONFIG2 608.shield --> --> rxCONFIG2 AUX Channel txAuxCh+ 610 --> --> rxAuxCh+ (p) Ground txGNDaux 604.shield --> --> rxGNDaux (pin 16) AUX Channel txAuxCh− 610.b --> --> rxAuxCh− (n) Hot Plug txHPD 610.shield --> --> rxHPD Return txGNDpwr 604.shield GND --> rxGNDpwr DP_PWR txDP_PWR 602.shield +5 V --> rxDP_PWR

FIG. 8 shows a STP DisplayPort Cable 102.6 based on Shielded Twisted Pair (STP) technology, including a sixth Input Paddle Board 114.6, a sixth Raw Cable 108.6, and a sixth Output Paddle Board 116.6 according to an embodiment of the invention. The sixth Raw Cable 108.6 includes a total of five STPs 702, 704, 706, 708, and 710, each comprising a shield and two signal wires “a” and “b” as described in FIG. 1A.

The allocation of the DisplayPort signals to connections through the sixth Raw Cable 108.6 is provided by configurations of the sixth Input and Output Paddle Boards 114.6 and 116.6 respectively, and is analogous to the allocation in the Coax DisplayPort Cable 102.5, FIG. 7. The STP signal assignments are illustrated in FIG. 8 which is identical to FIG. 7 except for showing Shielded Twisted Pairs (STPs) 702, 704, 706, 708, and 710 instead of coax pairs 602-610. While the sixth Input and Output Paddle Boards 114.6 and 116.6 have similar connectivity to the corresponding fifth Input and Output Paddle Boards 114.5 and 116.5, their mechanical properties would differ in order to accommodate the different termination geometries of the STPs versus the coax pairs on the paddle boards.

All auxiliary signals, CONFIG1, CONFIG2, Hot Plug, Ground and DP_PWR, may be placed over any shields of coaxial or STP lines as may be convenient or for an arrangement that may be adapted to best utilize the space on the paddle boards and the configuration of the respective connectors.

Low Wire Count Summary

The number of wires in a boosted high speed digital video cable such as an HDMI or DisplayPort cable, has been reduced from fourteen or more in prior art cables to nine or ten by using the shields to individually carry active signals as well as power and ground. This reduction is enabled by the boost device which guarantees the removal of potentially harmful common mode interference on the high speed data lines. The reduction in the number of wires simplifies their alignment for termination in the connectors. The original high speed cables use a mix of coaxial lines or shielded twisted pairs and standard wires. The invention provides a reduction in the construction cost of high speed cables by the use of only a single type of wire, either coaxial or STP, to carry all signals. This significantly simplifies cable assembly and allows a single step termination process, ultimately reducing cost.

Low Impedance Cables

In addition to the advantages obtained through the low wire count technique described above, a further cost advantage may be achieved by using coaxial lines or Shielded Twisted Pairs (STP) of a lower impedance than the nominal line impedance implied in the standards, for carrying the high speed data signals in any of the Boosted Digital Video Cables 102 described here.

FIG. 9 shows a three coax line cross sections, to illustrate a comparison between exemplary design choices, including a standard coax 902; a reduced-outer-diameter coax 904; and an increased-core-diameter coax 906. The standard coax 902 comprises an outer insulating sheath 902.a, a shield 902.b, an inner insulator 902.c, and a core wire (core) 902.d. The reduced-outer-diameter coax 904 comprises an outer insulating sheath 904.a, a shield 904.b, an inner insulator 904.c, and a core wire (core) 904.d. The increased-core-diameter coax 906 comprises an outer insulating sheath 906.a, a shield 906.b, an inner insulator 906.c, and a core wire (core) 906.d.

The characteristic impedance Z0 of a coaxial line is determined by dimensions of the cable, more precisely, by the ratio of the diameter of the core wire to the inner diameter of the shield, and by the dielectric constant of the inner isolator material.

The core 902.d of the thin standard coax 902 with a characteristic impedance of 50 ohms is an American Wire Gauge (AWG) wire of about 78 μm diameter, resulting in an overall diameter of the standard coax 902 of about 210 μm.

By allowing the coax to have a lower, “non-standard” characteristic impedance it is possible for example, and without changing the insulator material, to either reduce the outer diameter of the coax without having to use a finer core wire, or to increase the core diameter while keeping the outer diameter constant.

The core 904.d of the reduced-outer-diameter coax 904 is the same wire gauge as the core 902.d of the standard coax 902, but the shield 904.c is shrunk such that a characteristic impedance of 35 ohms is obtained for the reduced-outer-diameter coax 904. This results in an overall diameter of the reduced-outer-diameter coax 902 of about 145 μm, a savings of about 30% compared to the standard coax 902 with 50 ohm characteristic impedance.

If the outer diameter is not changed, a thicker core wire may be used. The shield 906.b, hence the overall diameter of the increased-core-diameter coax 906, corresponds to that of the standard coax 902. However, the thickness of the core 906.d is increased such that a characteristic impedance of 35 ohms is obtained for the increased-core-diameter coax 906, resulting in a wire size of AWG 40 for the core 906.d of the increased-core-diameter coax 906. AWG 35 corresponds to a wire diameter of about 143 μm, an almost 80% increase in thickness.

The inventors have considered the impact of deviating from the standard 50 ohm coax for implementing the HDMI and DisplayPort cables described above, that is the Basic Coax HDMI Cable 102.1, the HEAC-Capable Coax HDMI Cable 102.3, and the Coax DisplayPort Cable 102.5, as well as other boosted digital video cables. To recapitulate, the Video Source Device 104 transmits high speed differential signals through coax pairs to the Cable Boost Device 118 which equalizes and boosts the signals before transmitting them to the Video Sink Device 106.

The Video Source Device 104 is designed to transmit these high speed differential signals over cables presenting a characteristic impedance of 100 ohms differentially, that is 2 times 50 ohms in the case of dual coaxial lines (coax pairs). An input circuit in the Video Sink Device 106 similarly presents matching 100 ohms differential terminations to the cable.

In the case of the boosted cables with a reduced impedance coax, the Cable Boost Device 118 provides a proper output circuit for transmission of the boosted signals to the Video Sink Device 106. An input termination in the Cable Boost Device 118 can be tuned to terminate a reduced impedance cable with the correct impedance, for example 35 ohms, or 70 ohms differentially.

The Video Source Device 104 is designed as a current source and would be able to directly transmit into any cable impedance; no undesired signal reflections would result as long as the cable is correctly terminated at the receiving end, that is at the Cable Boost Device 118. However, compliance testing of HDMI and DisplayPort cables requires the cable to present a nominal 100 ohm differential impedance at source end for a unidirectional active cable and both ends for a passive cable.

FIG. 10 shows a Low-Impedance (Low Z0) Coax HDMI Cable 102.10 which is identical to the Basic Coax HDMI Cable 102.1 of FIG. 3 except for a Low-Impedance Input Paddle Board 114.10 which replaces the first Input Paddle Board 114.1. The Low-Impedance Input Paddle Board 114.10 has the same connectivity as the first Input Paddle Board 114.1, except for eight padding resistors R1 to R8 which are inserted between the high speed signal terminals txD2+, txD2−, txD1+, txD1−, txD0+, txD02−, txCK+, and txCK− of the Input Connection Field 212, and the inner signal wires “a” and “b” of the corresponding coax pairs 202 to 208 of the first Raw Cable 108.1.

One pair of padding resistors is required to be inserted in series with each of the inner signal wires “a” and “b” of the TMDS signals. The resistance of each padding resistor is derived such that the combined resistance of two padding resistors in series with the inner signal wires (the shielded conductors) of each coax pair (dual shielded cable element) 202 to 208 is equal to the difference between the specified nominal cable impedance and the impedance of the coax pair, for example a 100 ohm nominal impedance is achieved by using two coax lines of 35 ohm impedance, each with 15 ohm padding resistors, as a coax pair.

The padding resistors R1-R8 could be omitted without loss of functionality, but they are provided in order to meet the specified differential input impedance of 100 ohms for the Low-Impedance Coax HDMI Cable 102.10.

If the coax pairs 202 to 208 of the first Raw Cable 108.1 are made of low-impedance coaxial lines, such as the reduced-outer-diameter coax 904 or the increased-core-diameter coax 906 which each have an exemplary characteristic impedance of 35 ohms, the values of each of the padding resistors R1 to R8 should be 50−35=15 ohms, such that each coax pair, combined with the padding resistors, presents a 2×50=100 ohm impedance to the differential terminals of the Input Connection Field 212. In general, the resistance of each padding resistor R1 to R8 should be X ohms, where X is equal to the difference between one half of the specified nominal impedance (e.g. 100 Ohms for HDMI) and the actual characteristic impedance of the coax.

Similarly, other coax based high speed video cables such as the HEAC-Capable Coax HDMI Cable 102.3 (FIG. 5) and the Coax DisplayPort Cable 102.5 (FIG. 7) are easily modified by the addition of the padding resistors R1 to R8 on their respective input paddle boards, to accommodate low-impedance coax cables.

It is worth noting that signals other than the high speed differential data signals, for example the HEAC channel of HDMI and the AUX channel of DisplayPort, are not boosted by the Cable Boost Device 118. The coax pairs transporting these signals (coax pair 410 for HEAC, and coax pair 610 for the AUX channel) can not be of the low-impedance type, but must be regular 50 ohm coaxes.

The same techniques for using reduced impedance coax cables also applies for boosted HDMI and DisplayPort cables that use Shielded Twisted Pairs (STP) for transmitting the high speed differential data signals. The characteristic impedance of STPs is determined by the ratio of the insulated wire diameter to the diameter of the bare wire, and the dielectric properties of the insulation material.

Low-impedance STPs are easily made by reducing the thickness of the insulation compared to the diameter of the bare wire. This of course also affects the size of the shield. A reduction in the thickness of STP wire insulation by about 30% without changing the bare wire thickness will reduce the (differential) impedance of the STP from a nominal 100 ohms to 70 ohms. Instead of reducing the size of the STP cable in this way, it is also possible to maintain the original overall size and increase the bare wire thickness.

When a low impedance STP is employed in any of the boosted video cables based on STP technology, such as the Basic STP HDMI Cable 102.2 (FIG. 4), the HEAC-Capable STP HDMI Cable 102.4 (FIG. 6), and the STP DisplayPort Cable 102.6, the same considerations as with the coax based cables apply: the input circuit of the Cable Boost Device 118 should be programmed to match the STP impedance, and the input paddle board should be modified to include padding resistors. Similar to the rule that applies in the coax case, the resistance of each padding resistor R1 to R8 in the STP case should be Y ohms, where Y is equal to one half of the difference between the specified nominal impedance (e.g. 100 Ohms for HDMI) and the actual differential impedance of the STP.

The lowering of the characteristic impedance in coax or STP based cables which include boost devices has a number of advantages which may be exploited, either to reduce the size of the cable for material savings, improved flexibility, etc., or to increase the wire size without reducing the overall size of the cable for improved handling, and lower material cost. Note that thicker wire may actually cost less to produce than very fine wire.

Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.

A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow. 

What is claimed is:
 1. A digital video cable for carrying one or more high speed differential digital data signals and one or more auxiliary signals between a video source device and a video sink device according to a cable specification, the cable comprising; a raw cable having one or more dual shielded cable elements, each dual shielded cable element comprising a shield and two shielded conductors for transmitting two polarities of a high speed differential digital data signal, an impedance of at least one dual shielded cable element being lower than a nominal impedance of the cable specified in the cable specification; a first circuit carrier connecting the video source device to the raw cable, the first circuit carrier including two padding resistors, each padding resistor being electrically coupled between a respective shielded conductor of the at least one dual shielded cable element and the video source device; and a second circuit carrier connecting the raw cable to the video sink device, the second circuit carrier including a boost device for terminating the at least one dual shielded cable element and boosting the high speed differential digital data signal carried by said at least one dual shielded cable element, an output of the boost device being connected to the video sink device.
 2. The cable as described in claim 1, wherein a combined resistance of the two padding resistors is substantially equal to a difference between the nominal impedance and the impedance of the at least one dual shielded cable element.
 3. The cable as described in claim 2, wherein the padding resistors are of equal resistance.
 4. The cable as described in claim 1, wherein said one or more dual shielded cable elements are dual coaxial elements, each comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor.
 5. The cable of claim 4, wherein the raw cable comprises said one or more dual shielded cable elements only, each dual shielded element comprising a Shielded Twisted Pair (STP), comprising a shield enclosing the two shielded conductors.
 6. The cable as described in claim 4, wherein the nominal impedance of the cable is 100 ohms, and the impedance of said at least one dual shielded cable element is from about 50 ohms to about 90 ohms, comprised of characteristic impedances of the two coaxial lines.
 7. The cable as described in claim 6, wherein a characteristic impedance of each coaxial line is about 35 ohms.
 8. The cable as described in claim 1, wherein some of said one or more dual shielded cable elements are dual coaxial elements, each comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor.
 9. The cable of claim 1, wherein the raw cable comprises said one or more dual shielded cable elements only, each dual shielded element comprising a dual coaxial element, comprising two coaxial lines whose shields are joined, each coaxial line enclosing one shielded conductor.
 10. The cable as described in claim 1, wherein said one or more dual shielded cable elements are Shielded Twisted Pairs (STP), each STP comprising a shield enclosing the two shielded conductors.
 11. The cable as described in claim 10, wherein the nominal impedance of the cable is 100 ohms, and a characteristic impedance of a Shielded Twisted Pair is from about 50 ohms to about 90 ohms.
 12. The cable as described in claim 11, wherein the characteristic impedance of the Shielded Twisted Pair is about 70 ohms.
 13. The cable as described in claim 1, wherein some of said one or more dual shielded cable elements are Shielded Twisted Pairs (STP), each STF comprising a shield enclosing the two shielded conductors.
 14. The cable as described in claim 1, wherein the cable specification is the High-Definition Multimedia Interface (HDMI) standard.
 15. The cable as described in claim 14 wherein, said one or more high speed differential digital data signals comprise Transition Minimized Differential Signaling (TMDS) signals; and said one or more auxiliary signals comprise Consumer Electronics Control (CEC), Serial Clock (SCL), Hot Plug Detect (HPD), and +5V Power signals.
 16. The cable as described in claim 15, wherein the boost device comprises an equalizer and an amplifier for equalizing and boosting the TMDS signals respectively.
 17. The cable as described in claim 14, wherein: the shielded conductors of four dual shielded cable elements extending between the video source device and the boost device; the shielded conductors of the four dual shielded cable elements are adapted to carry respective four high speed differential digital data signals, which are Transition Minimized Differential Signaling (TMDS) signals; the shielded conductors of one other dual shielded cable element, extending between the video source device and the video sink device, are adapted to carry an auxiliary signal, which is a HDMI Ethernet and Audio Return Channel (HEAC) differential signal; and the shields of the four dual shielded cable elements and said one other dual shielded cable element are adapted to carry auxiliary signals; which are Consumer Electronics Control (CEC), Serial Clock (SCL), Serial Data (SDA), Digital Data Channel (DDC)/CEC Ground, and +5V Power signals.
 18. The cable as described in claim 1, wherein the cable specification is the Displayport standard.
 19. The cable as described in claim 18, wherein: the shielded conductors of four dual shielded cable elements extending between the video source device and the boost device; the shielded conductors of the four dual shielded cable elements are adapted to carry respective four high speed differential digital data signals, which are Main Line lanes; the shielded conductors of one other dual shielded cable element, extending between the video source device and the video sink device, are adapted to carry an auxiliary signal, which is an Auxiliary Channel (AUX CH) differential signal; and the shields of the four dual shielded cable elements and said one other dual shielded cable element are adapted to carry auxiliary signals, which are CONFIGI, CONFIG2, Ground, Hot Plug Detect (HPD), and DisplayPort power (DP-PWR) signals.
 20. The cable as described in claim 19, wherein the boost device comprises an equalizer and an amplifier for equalizing and boosting the Main Line lanes respectively.
 21. The cable as described in claim 1, wherein a shield of one of said one or more dual shielded cable elements is adapted to carry an auxiliary signal.
 22. The cable as described in claim 21, wherein the two shielded conductors of one of said one or more dual shielded cable elements are adapted to carry a high speed differential digital data signal.
 23. A method for transmitting a high speed differential digital data signal from a video source device to a video sink device over a digital video cable designed to meet a cable specification, the method comprising: coupling two respective padding resistors between two polarities of the high speed differential digital data signal and an input of a raw cable, which has an impedance lower than a nominal impedance of the cable specified in the cable specification; coupling a differential output signal from an output of the raw cable to a boost device whose input matches the impedance of the raw cable; boosting the differential output signal to generate a boosted differential signal; and coupling the boosted differential signal to the video sink device.
 24. The method described in claim 23 further including transmitting an auxiliary signal from the video source device to the video sink device over a shield of the raw cable.
 25. The method described in claim 24, wherein the transmitting comprises transmitting over a coaxial cable having a pair of coaxial lines whose shields are joined; including transmitting the auxiliary signal over the joined shields.
 26. The method described in claim 24, wherein the transmitting comprises transmitting over a Shielded Twisted Pair (STP) comprising a shield enclosing two shielded conductors, including transmitting the auxiliary signal over the shield of the STP, and transmitting the high speed differential digital data signal over the two shielded conductors. 